Noise control and moisture management constitute two rapidly growing economic and public policy concerns for the construction industry. Areas with high acoustical isolation (commonly referred to as ‘soundproofed’) are requested and required for a variety of purposes. Apartments, condominiums, hotels, schools and hospitals all require rooms with walls, ceilings and floors that reduce the transmission of sound thereby minimizing, or eliminating, the disturbance to people in adjacent rooms. Soundproofing is particularly important in buildings adjacent to public transportation, such as highways, airports and railroad lines. Additionally theaters, home theaters, music practice rooms, recording studios and others require increased noise abatement. Likewise, hospitals and general healthcare facilities have begun to recognize acoustical comfort as an important part of a patient's recovery time. One measure of the severity of multi-party residential and commercial noise control issues is the widespread emergence of model building codes and design guidelines that specify minimum Sound Transmission Class (STC) ratings for specific wall structures within a building. Another measure is the broad emergence of litigation between homeowners and builders over the issue of unacceptable noise levels. To the detriment of the U.S. economy, both problems have resulted in major builders refusing to build homes, condos and apartments in certain municipalities; and in widespread cancellation of liability insurance for builders. The International Code Council has established that the minimum sound isolation between multiple tenant dwellings or between dwellings and corridors is a lab certified STC 50. Regional codes or builder specifications for these walls are often STC 60 or more.
In addition the issue of noise control, fire resistance is an equally important construction industry concern. In fact, the primary objective of today's model building codes is ensuring that building occupants are safe from fire. The model building codes such as that of the International Code Council (ICC) or the National Fire Protection Association (NFPA) are written so that buildings will protect occupants who aren't intimate with the initial fire development for as long as they need to evacuate, relocate, or defend themselves in place. Buildings are also designed to provide firefighters and emergency responders with a reasonable degree of safety during search and rescue operations, and reasonably protect people near the fire from injury and death. Finally, the codes intend to protect adjacent buildings from substantial damage during a fire. These building codes use fire resistance to create safe structures in a strategy is known as compartmentation. The concept is to prevent a fire from spreading from the compartment of origin to an adjacent compartment for a prescribed length of time. For this purpose, a compartment can be defined in many ways: such as the occupied rooms of multi-family dwellings; as an entire building or some portion of a building (e.g. one floor in a high-rise); or as a single room like a hotel room. Buildings with mixed or multiple occupancies may be divided either vertically or horizontally into separate occupancies by fire-resistance-rated construction.
It is obvious that the problem is compounded when a single wall or structure needs to effectively both abate high noise levels and offer superior fire resistance.
For example, a traditional method for ensuring the fire resistance of a wall assembly is though the use of multiple layers of specially formulated gypsum wallboard. This wallboard, termed type X by the manufacturer, has a high density core reinforced with fiberglass fibers and sold in typical thicknesses of ⅝ inch and 1 inch. Major US manufacturers of type X gypsum include United States Gypsum of Chicago, Ill., National Gypsum of Charlotte, N.C., Georgia Pacific of Atlanta, Ga. and Lafarge of Paris, France. The conflict in the two requirements is evident in the case of many typical wood framed wall assemblies. A single stud wall assembly with a single layer of type X gypsum wallboard on each side is recognized as having a one-hour rating. Similarly, a single stud wall assembly with two layers of type X gypsum wallboard per side has a two-hour fire resistance rating. Unfortunately, while these example walls may meet or exceed the fire resistance requirements of the applicable building code, their acoustical performance is inadequate. That same single stud wall with a single layer of type X gypsum wallboard has been laboratory tested to an STC 34—well below code requirements. A similar wall configuration consisting of two layers of type X gypsum wall board on one side and a single layer of type X gypsum board on the other is an STC 36—only a slightly better result. Obviously, type X gypsum wallboard is an excellent fire resistive element, but a poor acoustical material. Other systems for improving the acoustical performance do exist, including mass loaded vinyl, resilient channels, and sound isolating clips. However, these techniques only add steps and materials to the assembly and do not contribute in any way to the final assembly's fire resistance.
Accordingly, what is needed is a new material and a new method of construction to reduce the transmission of sound from a given room to an adjacent area while simultaneously providing adequate fire resistance.